1. Field of the Invention
The invention relates to a variable valve actuation apparatus for an internal combustion engine.
2. Description of Related Art
A variable valve actuation apparatus for an internal combustion engine mounted on a vehicle, such as an automobile, includes a variable valve timing mechanism. The variable valve timing mechanism is hydraulically actuated in order to change the valve timing of an engine valve, such as an intake valve and an exhaust valve.
In the variable valve actuation apparatus for an internal combustion engine, the relative rotation phase of a camshaft with respect to a crankshaft is changed by actuating a movable member of a variable valve timing mechanism fixed to one end of the camshaft by supplying and draining oil to and from the variable valve timing mechanism. In this way, the valve timing of the internal combustion engine is changed by changing the relative rotation phase of the camshaft with respect to the crankshaft.
The variable valve actuation apparatus for an internal combustion engine includes a hydraulic circuit and an oil control valve. The hydraulic circuit connects the variable valve timing mechanism with an oil pump. The oil control valve is provided halfway in a plurality of oil passages that constitute the hydraulic circuit. The oil control valve controls hydraulic pressure that acts on the movable member of the variable valve Liming mechanism. The oil control valve controls hydraulic pressure that acts on the movable member of the variable valve timing mechanism by changing the mode in which oil is supplied to and discharged from the variable valve timing mechanism through the plurality of oil passages that constitute the hydraulic circuit. In this manner, the oil control valve actuates the movable member.
For information, Japanese Patent Application Publication No. 2012-67699 (JP 2012-067699 A) describes a bolt-integrated oil control valve, that is, the function of a bolt that fixes a movable member of a variable valve timing mechanism to a camshaft is added to an oil control valve. The bolt-integrated oil control valve is screw-fastened to one end of the camshaft. Thus, the bolt-integrated oil control valve fixes the movable member of the variable valve timing mechanism to the camshaft.
When the bolt-integrated oil control valve is employed, the length of each of portions of the oil passages of the hydraulic circuit between the oil control valve and the variable valve timing mechanism is reduced. As a result, it is possible to improve the response at the time of hydraulically actuating the movable member of the variable valve Liming mechanism and to prevent or reduce leakage of oil from the portions of the oil passages of the hydraulic circuit between the variable valve timing mechanism and the oil control valve.
However, in the case where the bolt-integrated oil control valve is employed, when the oil control valve is removed for replacement, or the like, fixing of the movable member to the camshaft by screw fastening using the oil control valve is also released, with the result that the movable member is also compelled to be removed from the camshaft.
A fixed position of the movable member in a rotation direction around the axis of the camshaft in the variable valve timing mechanism influences the relative rotation phase of the camshaft with respect to the crankshaft. For this reason, at the time of fixing the movable member, removed as described above, to the camshaft again, the movable member and the camshaft need to be accurately positioned in the rotation direction around the axis of the camshaft.
Therefore, when a replacement oil control valve is fixed to the camshaft by screw fastening together with the variable valve timing mechanism (movable member), the movable member needs to be accurately positioned with respect to the camshaft in the rotation direction around the axis of the camshaft. As a result, work for such positioning takes much effort, so the replacement workability of the oil control valve decreases.